The present invention relates to an improved transducer bridge circuit arrangement and to a method for accomplishing the improvement. The invention is generally useful for bridge circuits and is especially useful in electronic scales.
Many strain gauge load cell scales are being produced today, employing a plurality of load cells in respective bridge circuit configurations. A "load cell" in this context is considered to be a bridge circuit arrangement comprising four strain gauge elements. For example, one load cell may be employed at each corner of a platform scale. The load capacity of present day scales covers a wide range of approximately 10 lbs. to over 200,000 lbs. In virtually all scales where a high weighing accuracy is required, some adjustment must be made on each of the individual load cells to assure that the proper scale performance is achieved independently of the point where the weight or load is applied to the scale.
Heretofore it has been conventional to connect potentiometers in series with the supply voltage input terminals of each individual transducer bridge circuit load cell. The adjustment of these potentiometers effectively adjusts the sensitivity of the individual transducer bridge, thereby matching the sensitivity to that of the other transducer bridges used in a multi-cell bridge system.
The use of a plurality of potentiometers is expensive because it requires not only the addition of expensive potentiometers. It also requires substantial time necessary for the adjustment which may have to be repeated several times until a bridge circuit arrangement comprising a plurality of individual bridges has been adjusted as required. Further, the use of such potentiometers decreases the system reliability because potentiometers are inherently unreliable especially where the scales are used in an environment which is not advantageous for the operation of the potentiometers. For example, moisture and dirt may enter into the potentiometers thereby still further reducing their reliability.